The work presents a comprehensive and interdisciplinary approach to the legal issues of liberalization and energy security in the gas market. The author analyzes legal issues as well as economic and geopolitical ones which are of particular importance to Polish position in the common EU gas market, especially in the case of dependency on one main gas supplier. The information and research findings presented in the study highlight some aspects not hitherto made lucid, while significantly influencing the issues of energy security. This relates, for example, to the free movement of goods, TPA principle (that of free and unhindered access to gas infrastructure), or to the regulation of infrastructural monopolies, including unbundling of independent system operators. The study with its interdisciplinary approach fits well with the current geopolitical situation of Poland as a significant gas importer from the Eastern direction. The book is intended for practitioners who have influence on decision making processes in the area of liberalization of domestic energy market and the state's energy security as well as for students and legal theorists interested in the EU law institutions and economic law related to gas market. The study can also be useful for students and professors of political science and management science who want to find out more about the structure and relationships between the state and entrepreneurs in the gas market dominated by infrastructural monopolies.